Electron tube with apertured interdigital delay line, adjacent apertures being of different size and at different voltages



1966 R. c. HERGENROTHER 3,

ELECTRON TUBE WITH APERTURED INTERDIGITAL DELAY LINE, ADJACENT APERTURES BEING OF DIFFERENT SIZE AND AT DIFFERENT VOLTAGES Filed April 26, 1963 2 Sheets-Sheet 1 //V VE/V T0,? RUDOLF C. HERGENROTHEH ATTOHWE Y 1966 R. c. HERGENROTHER 3,

ELECTRON TUBE WITH APERTURED INTERDIGITAL DELAY LINE, ADJACENT APERTURES BEING OF DIFFERENT SIZE AND AT DIFFERENT VOLTAGES 2 Sheets5heet 3' Filed April 26, 1963 /V VE/V 70/? RUDOLF C HERGE/V/POTHER 5y v 1 ATTORNEY United States Patent G ELECTRON TUBE WITH APERTURED INTER- DIGITAL DELAY LINE, ADJACENT APER- TURES BEING OF DIFFERENT SIZE AND AT DIFFERENT VOLTAGES Rudolf C. Hergenrother, West Newton, Mass., assignor to Raytheon Company, Lexington, Mass., a corporation of Delaware Filed Apr. 26, 1963, Ser. No. 275,942 7 Claims. (Cl. 315-35) This invention pertains generally to electron tubes of the traveling wave type, and more particularly to electrostatically focused traveling wave tubes and interdigital delay lines therefor. While the invention is applicable to traveling wave tubes utilizing either forward or backward wave phenomena, the description that follows is directed to backward wave oscillators as being exemplary of other tubes and circuits to which the invention is applicable.

The interdigital delay line, which has a backward wave fundamental mode, has found utility as the delay element in backward wave oscillators and amplifiers. In such electron tubes the electron beam is focused by passing through circular apertures inthe delay line interdigitated fingers. The circular apertures are centered on the beam axis of the electron beam. Alternate fingers of the delay line are connected to respective higher and lower potential sources as more specifically described in my co-pending US. patent application Serial No. 64,790. In such interdigital electrostatically focused periodic delay lines the circular apertures have equal diameters. As the electron beam passes through successive apertures of uniform diameter but alternately higher and lower potential, the beam tends to alternately expand and contract in' diameter because of the well known effect of such higher and lower potentials on an electron particle. This expansion and contraction of the beam produces a scalloping effect on the beam and has a detrimental side effect in that unavoidable collisions between the electron beam and the apertured fingers occur predominantly at the lower potential fingers. When the electron beam collides with a finger, secondary emission of electrons from the surface of the finger occurs. These secondary emissions are undesirable in that they enter the electron beam and cause current loading of the delay line tuning circuit, they absorb radio frequency power and they contribute to the generation of spurious oscillations within the delay line structure.

Accordingly, it is an object of the invention to minimize the adverse efiect of secondary emission in such delay line structures. To this end, the invention provides a delay line having interdigitated fingers with adjacent apertures of unequal diameter. The aperture diameter of the higher potential fingers is less than the aperture diameter of the lower potential fingers so that collision between the electron beam and the apertured fingers occurs predominantly at the higher potential fingers. The higher potential fingers are at a relatively positive potential with respect to the adjacent lower potential fingers. Secondary electrons are at a much lower velocity than the primary electrons of the electron beam. Consequently, such electrons as are caused to be emitted from the surface of the higher potential fingers by collision of the electron beam with the fingers are more susceptible to the influence of the higher potential electrostatic field and will be eifectively suppressed or attracted back to the surface of the higher potential fingers, thereby avoiding the adverse effect of such secondary emissions if allowed to interact with the electron beam as noted in the aforementioned prior art structures.

In accordance with the present invention, the above 3,289,93fi Patented Nov. 29, 1966 and other objects are achieved by means of a traveling wave tube structure including an envelope, a delay line therein having a plurality of interdigitated fingers each having an apertured portion, with such apertured portions being alternately larger and smaller in size and lying in registry with each other and with a beam of electrons produced by an electron gun, means for applying a higher potential to the smaller apertured fingers than to the larger apertured fingers next adjacent thereto to form an electron lens by means of each adjacent pair of fingers, and an output terminal for extracting R.F. energy from the delay line structure.

With the above considerations and objects in mind, the invention itself will now be described in connection with a preferred embodiment thereof given by way of example and not of limitation and with reference to the accompanying drawings, in which:

FIG. 1 is an elevation view of a backward wave oscillator structure in accordance with the present invention, with portions being broken away for clarity;

FIG. 2 is an enlarged transverse vertical section of the structure of FIG. 1;

FIG. 3 is an enlarged sectional view of the structure of FIG. 1;

FIG. 4 is a circuit diagram, including schematic representations of portions of the tube structure, illustrating one manner of applying voltages to certain elements of the structure of the present invention; and

FIG. 5 is a front view of one of the spacer elements of FIG. 3.

Referring now particularly to FIG. 1, a preferred form of backward wave oscillator tube structure in accordance with the present invention is shown as including an envelope 10 having at one end thereof a suitable base 12, such as a plug member adapted to be inserted in an octal socket, and including a plurality of connecting pins 14 and a central guide member 16 having a key 18 thereon. At the opposite end of the envelope 10 is at suitable finned section 20 which serves as a heat-dissipating means for transferring heat developed within the envelope 10 to the external atmosphere. Envelope 10 also includes an RF. output terminal 22, shown as a coaxial connector having an outer conductive member 24 and a central conductor 26, shown in dotted line in FIG. 1. It will be understood that the coaxial connector 22 is merely exemplary of other suitable output connector means which may be employed in place of the connector 22.

An electron gun indicated generally at 28 is mounted within envelope 10 near the base 12, such electron gun including a heater 30, a cathode 32 and an anode 34. As is customary, each of the electrodes of the electron gun 28 is connected to one or more of the pins 14 in the connector base 12 in order to be connected to the appropriate points in the circuitry connected to the tube socket into which the base 12 is inserted.

The beam of electrons formed by electron gun 28 is centrally disposed within the envelope 10 and extends from the electron gun 28 toward the right in FIG. 1, passing through the plurality of elements comprising the delay line 36. While only a portion of delay line 36 is shown in FIG. 1, it will be understood that the stacked tion of later figures, but it is convenient at this point to note that the line 36 is composed of a plurality of stacked elements, generally annular in form, and having a plurality of .interdig-itated fingers forming the electron lenses employed in the present invention for achieving focusing of the electron beam along the length of the envelope 10. One of the elements 38 making up delay line 36 is conductively connected to the center conductor 26 of coaxial output connector 22, and by this connection the RF. energy of a backward wave mode within envelope is conducted from element 38 through central conductor 26 to a suitable external circuit connected to coaxial connector 22.

FIGS. 2, 3, 4 and 5, taken together, show the structure of delay line 36 in greater detail. In general, delay line 36 is composed of two main portions, a lower portion 40 and an upper portion 42. The upper portion 42 is in electrical contact with, and mounted on, by means not shown, envelope 10, while lower portion 40 is mounted on and electrically insulated from port-ion 42 by means of nonconductive mounting members 43 and 44 which extend lengthwise along delay line 36. As a result of the slight- 1y smaller outside diameter of the arcuate periphery of portion 40, this portion of the delay line is insulated from the conductive envelope 10 by means of the semi-cylindrical space 46.

Delay line portion 40 comprises a plurality of conductive plate-like members 48, each of which includes a delay line finger 50 having an annular apertured portion 52 therein, as shown in FIG. 2, such plate-like members 48 being held together in stacked, spaced-apart relationship by means of a bolt 51 or the like and a plurality of spacing members 54. It should be noted that although a staoke form of delay line construction -is chosen herein as a preferred type of construction, other equivalent structures are within the scope and contemplation of the invention. For example, delay line portions 40 and 4-2 may be one piece castings rather than the laminations shown herein without departing from the scope of the invention.

The upper portion 42 of delay line 36 is similarly composed of a plurality of plate-like conductive members 58, each having a delay line finger 60 formed thereon, such fingers 60 lying in substantial registry with fingers 50 and having similarly disposed annular apertured por tions 62. The apertures 61 in fingers 60, however, unlike prior art structures, are smaller than the corresponding apertures 41 in adjacent fingers 50. Fingers 50 are connected to a source of lower potential than the potential on fingers 60 as will be subsequently shown in connection with FIG. 4. The plate-like members 58 of delay line portion 42 are similarly held together in stacked, spaced-apart relationship by means of bolts 59 and 57 or the like, along with a plurality of spacer members 66.

In operation, it should be noted that the resultant electron beam passing through apertured fingers 50 and 60 takes the form of a scalloped shape beam alternately increasing and decreasing in diameter in accordance with the respective alternately lower and higher potentials impressed across the apertures. Furthermore, as can be seen from FIG. 3, collision between the beam and the apertured fingers will occur predominantly at the higher potential, smaller diametered apertures 61 in fingers 69. Conversely, very few collisions will occur at the lower potential fingers 50. This scalloping effect is exactly opposite to that produced in prior art structures wherein the majority of collisions occur at the lower potential fingers in uniformly apertured delay line structures. Accordingly, in the delay line device of the invention, secondary emission caused by such collisions occurs predominantly on the higher potential fingers 60. Such secondary emissions as do occur are effectively suppressed or attracted back to the surface of the higher potential fingers by virtue of such higher potential.

Referring now to FIG. 4, an exemplary circuit is shown therein for applying appropriate voltages to the active elements of the backward wave oscillator structure of the prior figures. In FIG. 4, the delay line voltages are supplied by D.C. sources 70 and 72, indicated schematically as batteries in FIG. 4. The positive terminal of source 70 is connected to the upper delay line portion 42, having the smaller diameter apertures 61 therein, as well as to collector element 71. The negative terminal of source 70 is connected to the lower delay line portion 40 having the larger diameter apertures 41. This lower portion 49 is also connected to the positive terminal of D.C. source 72, the negative terminal of such source being connected to cathode 32. It will be understood that sources 70 and 72 are preferably made variable in order to provide means for effecting variable tuning and focusing of the electron tube. A third D.C. source 74 is connected between cathode 32 and anode 34, with its positive terminal being connected to anode 34 and its negative terminal being connected to cathode 32. A fourth source 81 supplies voltage to heater 30. 'By virtue of this circuitry a first D.C. potential designated generally as V is established between cathode 32 and delay line portion 40, with a second and greater D.C. potential designated generally as V being established between cathode 32 and delay line portion 42. The effective delay line voltage V is equal to the average of these two voltages V; and V that is to say The operation of the apparatus described here-in is similar in most respects to the operation of other backward wave mode structures, except that by virtue of the particular construction of the interdigi-tal delay line 36, and the application of the different D.C. voltages to the two portions 40 and 42 thereof, the necessity for supplying a magnetic focusing means is obviated, since focusing of the electron beam 76 is achieved electrostatically by means of the electron lenses formed between each adjacent pair of delay line fingers S0 and 60. With the beam thus focused along its length within the envelope 10, a backward wave mode is produced within the structure, and RF. energy is extracted from the structure through coaxial connector 22 for use in an external circuit.

Heretofore, in delay line structures of the type described in reference to FIGS. 1-4, secondary emission of electrons caused by collision between the electron beam and the apertured interdigitized fingers 40 and 42 took place predominantly on the lower potential fingers 50. In the present invention, however, by virtue of the unequally apertured fingers, substantially all of the beam collisions will occur at the higher potential fingers 60 where the secondary electrons produced by collision of the primary or beam electrons can be effectively suppressed and drawn back to the high potential fingers thereby reducing the adverse effects of secondary emission on the delay line structure. Such adverse effects include, among others, current loading of the delay line tuning circuit, loss of RF. power by absorption from secondary electrons and spurious oscillations within the delay line structure.

The invention has been described above in some detail, and particularly with reference to its application to backward wave oscillators. However, it will be apparent to those skilled in the art that the invention is also applicable to other structures employing an interdigital delay line, and in particular to other traveling wave devices. Accordingly, it is desired that this invention not be limited except as defined by the appended claims.

What is claimed is:

1. In a delay line structure:

a plurality of interdigitated members having alternately smaller and larger apertures therein;

and voltage means coupled to alternate interdigitated members such that the interdigitated members having the smaller apertures are at a higher potential than the interdigitated larger apertured members.

2. In combination:

envelope means;

a plurality of interdigitated apertured members disposed within said envelope, the size of the apertures in said interdigitated members being alternately larger and smaller;

means for directing a beam of electrons past said apertured members;

and means for applying a higher potential to the smaller apertured members and a lower potential to the larger apertured members.

3. Delay line means for focusing an electron beam comprising;

interlaced alternate and intermediate finger means, each of said finger means having an aperture therein located substantially at the beam axis of said electron beam, alternate finger means being coupled to a relatively higher potential source than said intermediate finger means, the size of the apertures being relatively smaller for the alternate finger means than the size of the apertures of the intermediate finger means so that collision between the electron beam and the delay line means occurs predominantly at the higher potential finger means thereby to prevent secondary emissions from entering the electron beam.

4. In combination:

envelope means;

an interdigital delay line within said envelope having a plurality of fingers each including an apertured portion, each of said apertured portions being in substantial alignment with one another, the size of the aperture in each finger being different than the size of the aperture in the finger next adjacent thereto;

means for applying to each of said fingers a voltage different from that applied to the fingers next adjacent thereto;

means for directing a beam of electrons past the aligned apertures of said fingers;

and means for extracting energy from said delay line.

5. In combination:

envelope-means;

an interdigital delay linewithin said envelope having a plurality of fingers each including an apertured .portion, each of said apertured portions being in substantial alignment with one another, the size of the aperture in each finger being difierent than the size of the aperture in the finger next adjacent thereto; means for providing a higher potential to the smaller of said different sized apertures than that applied to the larger of said different sized apertures; means for directing a beam of electrons past the aligned apertures of said fingers;

and means for extracting energy from said delay line.

6. In combination:

delay line means for focusing an electron beam comprising interlaced alternate and intermediate finger means, each of said finger means having an aperture therein located substantially at the beam axis of said electron beam, alternate finger means being coupled to a relatively higher potential source than said intermediate finger means, the size of the apertures being relatively smaller for the alternate finger means than the size of the apertures of the intermediate finger means so that collision between the electron beam and the delay line means occurs predominantly at the higher potential finger means thereby to prevent secondary emissions from entering the electron beam;

electron gun means for providing said electron beam and directing said beam past said interlaced fingers means;

potential source means for providing a first relatively high potential and a second relatively lower potential;

envelope means enclosing said delay line means and said electron gun means;

and means coupled to said delay line means for extracting energy from said delay line means.

7. A traveling wave electron discharge device having a plurality of interdigitated apertured members, the size of the apertures in said members being alternately larger and smaller, means for directing a beam of electrons past said apertured members, and means for applying a first potential to the smaller apertured members and a second potential to the larger apertured members, said first potential being greater than said second potential.

References Cited by the Examiner UNITED STATES PATENTS 7/1959 Kompfner 3153.6 2/1960 Hergenrother 3l539.3 X 

1. IN A DELAY LINE STRUCTURE: A PLURALITY OF INTERDIGITATED MEMBERS HAVING ALTERNATELY SMALLER AND LARGER APERTURES THEREIN; AND VOLTAGE MEANS COUPLED TO ALTERNATE INTERDIGITATED MEMBERS SUCH THAT THE INTERDIGITATED MEMBERS HAV- 